Wierd idle since Cobra intake install 1 year ago

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cobra98lsc

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About a year ago we put a 98 Cobra intake on the Mark, 98lSC

Every now and then at lights it idles like it has 1" lift on the cams,, sounds like a big block on steriods shakes the car around and is not missing at all just really rough.
If i put into neutral and bump the throttle it quits and smooths right out.
Also it never stalls.
Any ideas?
Checked all obvious, no vac leaks, cables wires all look good coils have all new boots etc.
Does this a couple times a day at say every other light or so.
Also mileage is down to about 20mpg highway. Not 24-25 i used to get with even with the 4.10's
Cleaned MAF
No codes.
Could it be time for O2 sensors they have 129,000 on them never been done.
 
RE: Wierd idle since Cobra intake install 1 year ago

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Could it be time for O2 sensors they have 129,000 on them never been done.
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I would R&R the O2s with that age/mileage and the loss of mileage, but I do not know if that will make any difference in the idle.
 
RE: Wierd idle since Cobra intake install 1 year ago

You know the funny thing is i did change that, but the Cobra is getting its air for the IAC from the plastic intake tube by the throttle body, so the air is metered, but i had to run that hose around the back of the manifold to make it look good, I wonder if i need a better or larger source for air to the IAC??

How is it plumbed on the Cobras? The stock 2nd gens was internal on the intake so no outside plumbing was needed that i can recall.
 
RE: Wierd idle since Cobra intake install 1 year ago

On the cobras there is a hose that goes in front of the intake to the IAC. That's how I hooked mine up.

You sure there's no leaks? When i first installed mine i cut one of the gaskets between the IMRC and the head. But after i shut the car off i could hear a soft sucking noise until the vaccum was depleted.
 
RE: Wierd idle since Cobra intake install 1 year ago

I might just pull the whole intake and re-install it.

Good thoughts on the gasket, it idles good sometimes and other times not but only since installing this intake,

I must have done something.

Also i am not running EGR anymore since intake either.
 
RE: Wierd idle since Cobra intake install 1 year ago

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Also i am not running EGR anymore since intake either.
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Nor am I. Make sure there's a good seal on the EGR delete plate too.
 
RE: Wierd idle since Cobra intake install 1 year ago

Might be the throttle body isn't returning all the way and/or the TPS is out of alignment??

mark
 
RE: Wierd idle since Cobra intake install 1 year ago

All good ideas,

ON that EGR delete i made it from aluminum plating...

I keep finding oil on the Fuel Pressure regulator wich is sandwiched right against the delete plate.. I wonder if that is dripping from the delete plate onto the FPR?

Hmmm i will remove plate and check out tonight and re-seal it all.

Did you notice any loss of mileage on the highway after your Cobra swap?

I gained 6 10ths at the track when i changed intakes,, i still dont beleive it but i went from running 14.60's conistently to 13.90's-14.10's all in same weather and same track. That 2nd Gen intake is crap.
 
RE: Wierd idle since Cobra intake install 1 year ago

Looks like I need to track down a Cobra intake and take care of my exhaust this spring if your running that fast.

Seems like I spoke to one other person recently that had a problem with the Cobra intake swap....but I can't remember who.
 
RE: Wierd idle since Cobra intake install 1 year ago

You will have to make an intake tube or use one from a Cobra
No EGR unless you weld and make your own tubes.
I made a blockoff plate from some aluminum stock and blocked it off.
You will have to relocate the cruise control module as the Mark8 throttle pulls from the front of the engine and the Cobra throttle body mounts upsidedown thus pulling from the rear, so you will need to make up a throttle bracket etc. Easy i just bent drilled and re-worked the mark 8 parts to fit so i retained cruise control etc.
Fuel rails from the 2nd Gen will work but the regulator hits right against the mounting boss for the EGR, so hence no EGR valve, re-route vac lines, and run a hose to intake tube from the IAC motor so the IAC is metered air or car wont even stay running.
Other than that it was the best single thing i ever did to this car.
Just revs smoother and much more quickly to gain RPM even in light throttle, doesnt feel like its straining to gain RPM.
 
RE: Wierd idle since Cobra intake install 1 year ago

Ford makes an EGR delete plate for about five bucks. Easier and better looking than making your own, IMO.

And make sure you get new gaskets between the IMRC's and heads.
 
RE: Wierd idle since Cobra intake install 1 year ago

EGR delete plate kit FORD part [strong]# E69Z-9D440-A[/strong] ~ went up to $10 - still worth it.
 
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